Will too many apps slow a smartphone down?

[Tymme]

Just like you can't say, for example, Facebook will use 100mb of data for this month, you can't say you need <number> apps before you slow down. It depends on a few things, like how much memory the program uses, how well it's coded (possible memory leaks), whether it stays running in the background, etc.

The more you add, the more likely it is to happen. If you get bored with an app and stop using it, uninstall it- you can always reinstall it later and data isn't removed.