It would if the joist a 2x6. The blocking is normally the same width as the floor joist.

No

Sure, it will.

Yes, it will...presuming all you mean by 'stiffening' is to prevent the joist from racking and warping.

Blocking does little to nothing to reduce deflection of joists.

Yes it does.

An oiverloaded joist will not fail straight down in deflection. It wil want to roll or twist first which then puts it in a postion where it is weaker than in perfect vertical alignment. This weaker positioning in turn lets it sag further.

The blocking does two things.
It prevents the rollover tendency, keepiung the joists in their strongest, vertical alignment.
It ties all the joist together so they act as a system/singulart unit instead of individually. I'm like a joist and you are too. You can lift more with help from your friends standing shoulder to shoulder.

Do you guys want to face off using caulking guns as the weapon of choice.....I have to agree with everyone. In the fact that the blocking (either type) keeps the joists from twisting , which does add to the sagging bafetr a bit it will help to stiffen the joists. Strictly speaking go for a wider joist of double every other one at the same width. This will definately stiffen the floor.....Smile.....MJH

Right it's better to solid block...

Solid blocking is fine to prevent joists from racking and twisting and warping...

But solid blocking does little or nothing to prevent deflection...or otherwise 'stiffen' floor joists.

Now you're making progress. Finish thinking it through...

You've admitted that blocking will " prevent joists from racking and twisting and warping..."

and since a straight and plumb joist will bear more without failing, it will provide for a stiffer floor.

The engineering agrees, too. That's why installation charts for joists specify what spans need blocking, bridging and furring. Leave it out and you don't meet the designed rating and risk failure.