There are two different subjects here and two different menus.
If power is on and you hold down all three switches, the Phone options menu will appear. If you continue holding the three switches until the menu disappears it will start to boot. This reset and then boot is identical to a battery pull.
If power is off and you hold down all three switches it calls up the the Boot Mode Selection Menu (displayed in character mode).
Boot Mode Selection Menu
Vol Up Selects, Vol Down Scrolls
Normal Powerup -- boot the Bionic
Recovery -- display (!) screen (then hold down vol Up/vol Down for Android System Recovery menu)
AP Fastboot -- developers only
BP SBF Flash -- developers only
BP Only -- developers only
BP HW Diag & Boot AP -- developers only
BP Tools -- developers only
If you do anything with this menu you open the door to causing permanent damage. This is sometimes referred to as BRICKing.
If you do nothing after a few seconds it will choose the current option (Normal Powerup) and boot your Bionic.
... Thom