To society as a whole, if everyone released their software as Free / Open Source software, much less effort would be wasted writing software that has already been written, and this effort could be directed towards developing better software to solve new problems.
However, FLOSS is a reverse tragedy of the commons situation. Everyone benefits from it, but the person who develops it isn't directly rewarded.
If your only motivation is profit (or you have a duty to maximise profit), there are still some good reasons to release FLOSS software: contributing to other infrastructure projects (especially if it is an established project) will be useful to other people who don't directly compete with you, and if there are lots of contributors, you will likely get more back than what you put in, while still getting the feature you want. In addition, if you make it known that your company is involved in FLOSS development, it is likely to generate good PR amongst technical people. It may also help you get good quality employees who are already familiar with some of your code base.
If your aim to make society a better place, without harming profits too much, rather than purely profit, FLOSS development makes even more sense. The risks to watch out for are spending too much time supporting the software, liability issues (nearly all FLOSS licenses include a disclaimer, but it is hard to rule out liability entirely), lowering barriers to entry, and having an unfair disadvantage if competitors use your code or ideas but don't release theirs (the Affero GPL can help with the former - and patenting novel algorithms and licensing them to all services which release their implementations with the latter - but you need to consider whether you have the cashflow to enforce your license / patents anyway).
If your only motivation is profit, ... there are still good reasons ...
It wouldn't not make sense for google to be developing top of the line web frameworks and open source them either; More better websites means more people would go on the internet and thus more google searches.
I think another reason you might open source software is so that the community around your product flourishes and uses your product even more.
To society as a whole, if everyone released their software as Free / Open Source software, much less effort would be wasted writing software that has already been written, and this effort could be directed towards developing better software to solve new problems.
However, FLOSS is a reverse tragedy of the commons situation. Everyone benefits from it, but the person who develops it isn't directly rewarded.
If your only motivation is profit (or you have a duty to maximise profit), there are still some good reasons to release FLOSS software: contributing to other infrastructure projects (especially if it is an established project) will be useful to other people who don't directly compete with you, and if there are lots of contributors, you will likely get more back than what you put in, while still getting the feature you want. In addition, if you make it known that your company is involved in FLOSS development, it is likely to generate good PR amongst technical people. It may also help you get good quality employees who are already familiar with some of your code base.
If your aim to make society a better place, without harming profits too much, rather than purely profit, FLOSS development makes even more sense. The risks to watch out for are spending too much time supporting the software, liability issues (nearly all FLOSS licenses include a disclaimer, but it is hard to rule out liability entirely), lowering barriers to entry, and having an unfair disadvantage if competitors use your code or ideas but don't release theirs (the Affero GPL can help with the former - and patenting novel algorithms and licensing them to all services which release their implementations with the latter - but you need to consider whether you have the cashflow to enforce your license / patents anyway).