I use the thanks button a lot. I hope it is received by others as a small token of appreciation for the work they do here. Many thankless people on the internet provide service to others with no pay. Many work in isolation. The wmf software makes it easy to thank these volunteers for the benefit they provide to me.
Many times I thank users for changes they made a long time ago, such as starting an important page. Some of the users I thank have not been active for years, I thank them just in case they ever check their account so they will know that someone appreciated the work they had done. When time permits, I also thank users who have contributed to pages that I started, or other pages that I come across in the hope of encouraging them to stick around. If I thanked you for your talkpage comment it is likely because I appreciate you taking the time to participate, not necessarily because I agree with you.
I try to limit thanking admins so as not to seem like I am looking for favours. Also, I have seen somewhere that some of the more popular users receive so many thanks that they view thanks as a form as harrassment. Please note that users can Mute other users by changing Notifications in their Preferences.
I wrote this mainly for those I have thanked to try and explain why I thank users. If you have any questions/concerns/remarks, I would appreciate you letting me know on my talk page. I will attempt to respond, time permitting.