When not to use VSTO for your future application?
I wanted to share some of my VSTO experience with you after spending an entire year in a team who is developing an application using VSTO.
Do use VSTO, and VSTO SE only if.
1- Your application performance does not matter at all, and you are totally happy if you’re Microsoft Word or Excel VSTO application starts in 30 sec or a min, or more.
http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1875348&SiteID=1
2- You have a large amount of memory (physical ram) that you want to waste.
https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=284446
3- It is totally ok if you lose all your opened Word documents when another Word VSTO application crashes.
If all the above makes sense to you please go ahead and VSTO your application, otherwise it is much better if you didn’t; I did a year ago, and I wish I never did; now I am suffering the consequences.
I wanted to write pages and pages of how wonderful VSTO development is, for example, the number developers you need do deploy the final application, you didn’t think it is one click, did you :-) , or more about the VSTO libraries, for example, if you insert an xml in a bookmark, you may randomly lose the bookmark with no explanation, or …
But I will leave it for you, if the team who developed VSTO never asked itself, why when I click on a real world VSTO application (not hello world) it takes 30 seconds to load, and why it didn’t release the memory when it is was closed , then it is pointless to go into further details.

