The ideal of gaining strength or muscle size is to progressively increase the weight or volume.
How can you safely do this without a spotter? Do you just tilt the bar to one side and let the weights fall to the ground if you can't get that rep up? Do you squat in the safety squat rack?
I see people in my gym doing the same weight month after month and year after year on the bench press. When i did powerlifting we always had a spotter and were able to increase the weights.
I have seen some modified bench presses online that allow people to bench alone and inrease weight with safety. I can tell by the OLD bench press machines in most gym most gym owners do not care or know about better bench press machines. It amazes how OLD this equipment is. The only way to make the most effective gains with the barbell bench press is to have a spotter.
Sure you can ask someone to spot, but the problem with that is you get different quality spotters every time. What an old sorry piece of equipment.