Today is the big day that Verizon started to roll out the dual OTA which brings your Galaxy S5 to Android 5.0 Lollipop. There are plenty of reasons to update to the latest firmware including security patches, new material design (new fluid animations, new color scheme, and 3d views), and also brings integration for Android for TV, cars, and wearables. There are also a few reasons you should consider not accepting the OTA update yet. This really only applies to those of you who care to root and mod your device.
For starters the root method for Kit Kat on the Galaxy S5 required you to flash the original kernel in Odin, then root, then flash the current kernel. Going from Kit Kat to Lollipop and then flashing a Kit Kat kernel over a Lollipop rom may not work. No one has tried it yet, and for now there may may not be a way to regain root.... ever... if you decide to accept the ota update.
Another reason you may consider not taking the update is the lack of Xposed support. With root and xposed framework you can pretty much modify your phone in any way without the need to unlock your bootloader and install a rom. Xposed is not supported past Kit Kat and there is no eta for when it may be updated with support for Lollipop.
If rooting and modding is not your thing then you should not blink at the chance to update and run Lollipop on your Galaxy S5. However if you do like to root and mod you should think twice before accepting the update. You have officially been warned.