Does it really make a difference?

[Bottomland OG]

Has anyone ever had a forcing cone lengthened on a gun and it made a noticeable difference in there pattern from before to after? I've had a couple done years ago but the only difference I noticed was that it helped a tad with recoil. I personally don't know enough about it to say one way or another. I was just wondering if maybe it might help more with certain guns.

[Wigsplitter]

Same here

[backforty]

I know it helps a great deal with buckshot not sure how that translates to bird shot.

[slicksbeagles1]

I have not personally had one done but, one of my friends that has a whole lot more money than me has had it done on several guns and I asked him if it was worth the money. His answer was not a nickels worth the difference, needless to say he saved me quite a bit of money.

[Gooserbat]

I've had two done before tss.  Helps lead shoot more even / less holes in the pattern.  I don't think it is as big a deal with tss.  I too noticed a little difference with recoil.

[Ihuntoldschool]

I wouldn't pay to have it done for patterns.  For recoil reduction it will help very slightly.

Lowers muzzle velocity slightly. 

Warm weather,  no issues.

Cold weather, just depends on the shell and the quality of the plastic used in the wads. 
Also depends how long you go. The longer the more chance wad won't seal the bore.