Belts should only be used during your heavy (>90% 1 rep maximum) squats and deads. And on heavy bench to hold down your bench shirt
Belts should not be used for anything else (even bent rows) as they have been proven to cause more injury in those situations by weakening you.
Here is a neat paper showing that belts do increase intra-abdominal pressure and produce less lower back shearing force than no belts, but notice the belts only separated out at the heaviest loads.
"Med Sci Sports Exerc 1990 Feb;22(1):117-26
The effectiveness of weight-belts during the squat exercise.
Lander JE, Simonton RL, Giacobbe JK
The purpose of this study was to examine the effectiveness of weight-belts during the performance of the parallel squat exercise. Six subjects were filmed (40 fps) as they performed three trials at each of three belt conditions (NB, none; LB, light; HB, heavy) in random order and three load conditions (70, 80, 90% 1RM (one repetition maximum] in increasing order. The parameters examined were collected and interfaced to a computer via an analog-to-digital (A/D) converter: ground reaction forces, intra-abdominal pressure (IAP), and EMG for the rectus abdominus (RA), external oblique (EO), and erector spinae (ES) muscles. Most differences were observed during the 90% 1RM condition, and only they are presented in this paper. Maximum IAP values were always greater (P less than 0.05) for the weight-belt conditions (LB, 29.2; HB, 29.1 greater th an NB, 26,8 kPa). Similar results were observed for the mean IAP. The integrated EMG (iEMG) activity of the muscles and adjusted mean values for back compressive force and back muscle force followed a similar but opposite pattern, with NB being the greatest. ES mEMG/(L5/S1) values for HB (18.1%) were the least, followed by LB (20.01%) and NB (22.3%). Few differences were observed between belt types.
These data suggest that a weight-belt can aid in supporting the trunk by increasing IAP."
I would suggest a real belt, best ordered online to avoid crap sold in sports stores. An Inzer belt is great. I'm a Titan man, and the Titan belt is very good. Lever belts and prong belts have been shown to be effective. Velcro belts microscopically slip and thus provide no real support; be careful.