I was always told to "reboot frequently because it keeps your RAM from filling up". I have found "frequently" to be a wide range. Plus we have the ability to clear the RAM when it starts to impact performance.
With my phone on stock 4.3 I could go weeks without needing a reboot (ie: I would reboot when things get laggy and a RAM clear doesn't fix it).
On stock 4.4.2 I had to reboot daily because my widgets would stop working constantly and lag was everywhere.
On 4.4.2 rooted n' tuned I can go weeks again without needing a reboot due to sluggish behavior.
It all depends on your specific phone. When you've exhausted all of your options to speed things up, it's time for a reboot.
I have found the app "Memory Booster" greatly helps my performance, allowing me to go even longer without a reboot.
Posted via Android Central App