I had themed TM which was about 200 MB large. Last night I decided to update it with the projects I carried out in the last 3 months (I wasn't sure my TM was up to date) and this morning I woke up with a 500 MB TM with 243k segments. So I decided to Upgrade it in the hope to reduce its size... 3 hours later I am left with a 900 MB TM containing the same number of segments.

Given my target language (Italian) I don't want to eliminate duplicate segments with different target because these target might be: with the informal you (tu), with the formal you in lower case (lei) and with the formal you capitalized (Lei). The end-clients have their preferences (capitalized you or not) and the informal you is used when the translation is target to a young audience.

However, I don't understand why the TM has doubled its size. What exactly did the Upgrade TM did? And did it differ from the TM Upgrade I did last night by selecting about a hundred of *.sdlxliff files? 

Should I do some maintenance to my TM to improve it? For example, can I see similar TUs to see if I can eliminate some of them because redundant?