I sometimes get performance questions that go something like "I want to frobnicate my kaboodle, and am considering doing this by flibitzing the wazoo, but I'm worried this might be too expensive".
The only way I know to answer such a question is, mu.
The problem is the phrase "too expensive". It is impossible to judge this without knowing what your limit is, ie. how rich you are. Any time you make a program do more work, that will cost time and usually also memory, but it would be silly to conclude we should do nothing at all! A game that does nothing may run infinitely fast, but it will not be very interesting to play.
Food costs money, but we must eat to survive. Sometimes I eat cheap food; other times I spend more to buy something more delicious. I recently ate at the Herbfarm for my wife Tracy's birthday. That was NOT cheap, certainly not something I could afford to do every day, and I will probably never go back, but it was a fantastic and memorable experience, totally worth it to celebrate a special occasion with special company.
Games are kinda like birthdays: good ones aim to be fantastic, memorable, special, exciting. That's hard to achieve if you're overly focused on saving a few bucks by getting takeout.
With game performance, unlike real life, there is no point trying to save wealth for a rainy day. When your goal is to run at a silky smooth 30 or 60 fps, that means you have either 33 or 16 milliseconds to complete each Update and Draw cycle. If you take longer you get a framerate glitch, but any time you take less, you just wasted some oomph that could have gone into making your game more exciting. It's not like you can save up leftover CPU cycles by spending just 5 milliseconds per tick, then cash in your 401k and spend it all at once when you hit retirement!
Note: the above is only true if you ignore battery life, which can be a reason for phone games to deliberately leave some processing time unused.
When trying to decide if you can afford to flibitz the wazoo, I would start by asking:
- Can you afford to do this extra work and still meet your framerate goals? This depends on how much other work your game is already doing, ie. how much performance headroom you have. If you aren't sure, now would be a good time to find out. If you have enough headroom, stop worrying and just go do it already!
- Can you afford NOT to do this extra work? If you cut the feature, will your game still be fabulous and spectacular?
- If you cannot afford to do the work, but also cannot afford not to do it, then welcome to game development :-) You now have two choices:
- Apply lateral thinking to find a cheaper way to achieve the same result
- Find ways to speed up or take out other less important work, thus winning back performance headroom which can be used to implement the new feature
Given a fixed amount of CPU cycles, the trick is not to avoid spending them, but to make sure you spend them wisely on things that will provide maximum bang for buck. Get this right, and gamers will be amazed by the stupendous awesomeness that ensues. Get it wrong, and they will think "meh, boring". This is more of an art than a science, but game developers must develop good instincts about which things are worth investing in.