yes and no - different bucks have different costs. Every dollar you spend is an investment, so you should be asking what return you're going to get for it. For example, if I add another developer, how much value will be created by the extra expense? If I buy a new sofa, how much value?
So, on the one hand, I agree with you that every dollar should be invested for maximum return, and it doesnt matter where it came from, but on the other hand, there are decisions to be made about going out and getting more capital above and beyond your retained earnings (i.e. debt or equity financing). That money comes at a much higher price, so the return on it has to justify the cost.
To put it in terms of an individual rather than a company, the decision to take out a mortgage to buy a house is connected but somewhat different than the decision of where to spend or invest your salary dollars. The mortgage is a loan that comes at a cost (the annual interest), yet it enables you to do something (buy a house)that you could not have done out of your earnings. So, many people choose that the return on owning a home (whether financial or otherwise) justifies the decision to seek out a source of capital beyond their earnings, even though that capital comes at a cost.
To put it in terms of an individual rather than a company, the decision to take out a mortgage to buy a house is connected but somewhat different than the decision of where to spend or invest your salary dollars. The mortgage is a loan that comes at a cost (the annual interest), yet it enables you to do something (buy a house)that you could not have done out of your earnings. So, many people choose that the return on owning a home (whether financial or otherwise) justifies the decision to seek out a source of capital beyond their earnings, even though that capital comes at a cost.