On the Xperia T at least, I can confirm that if you don't unify user data (get the zip from the lineageOS mint wiki), then the storage space indicated in the settings menu will be erroneous (on a fresh install it listed 13 Gb used out of a total of 14 Gb). Everything will install fine, but you will get this bug. If you adb shell into the phone and run "df -h /data", then the /data partition displays something like this:
Code:
Filesystem Size Used Avail Use% Mounted on
/dev/block/mmcblk0p14 1.9G 534M 1.4G 27% /data
If you unify user data first and then install LineageOS it should look something like this:
Code:
Filesystem Size Used Avail Use% Mounted on
/dev/block/mmcblk0p14 13G 940M 12G 8% /data
Note the size the /data partition is ~13 Gb and not ~2 Gb.
So, absolutely unify user data in TWRP before you install LineageOS if you've never done it before (if you're coming from a stock ROM). My advice would be to put it on an external microSD and flash it from there. I can confirm this works (I have 2 Xperia T's). On the first Xperia T I placed it on the internal SD partition and ran it from there. When I did this the script obviously failed, but it did actually create a unified partition by the looks of it. What happened was that the partition size was not being reported correctly (for whatever reason). But if you just carry on with the LineageOS install it will work fine.
But I recommend not going through this. Just do it "properly" and buy a microSD if you don't have one and flash it from there.
Also I'd like to add something that was difficult for me to find out: once you install TWRP you can usually boot into recovery and fix your phone if anything goes wrong. If you get to the Xperia logo screen then press the up and down volume buttons repeatedly (you prob only need to keep pressing one of them or the other, but this works regardless) and you will boot into recovery. From there you can adb push zips or mount a microSD with a zip and flash a ROM or anything else you need to do.