Thoughts on the optional third LOR?

[arrxing]

I am applying for bioengineering PhD programs this fall. A few of the programs I am applying to only require two LOR but allow an additional third letter of recommendation if you want to send one in. I know two of my letters are strong, but my third is not as strong. Would it be best for me to simply submit 2 LOR? Will I be at a disadvantage compared to other students with 3 LORs? 

[TakeruK]

We can only guess at what admissions committees at specific schools would actually do. But in general, if the requirement is 2, then there is no disadvantage if you only send 2. In my opinion, I would not send a 3rd letter unless the 3rd letter is similarly strong to the other 2 or it can say something really special/strong about you that the other 2 letter cannot.

[lyrehc]

Just be sure that both of the strong letters are actually written and sent. I decided to submit an extra reference because the graduate advisor for my master's program is very disorganized. I knew that if he got around to writing a letter that it would be good but didn't trust him to send it. He flaked and that extra letter made sure my file was complete and able to be reviewed.