Tens frames are a powerful visual aid in the math classroom at ANY level. The apparent lack of fluency with tens is the foundation of a whole raft of issues with place value understanding and the formation of part/whole concepts of number. Using tens frames helps the student form a powerful mental image of ten and tens which are used not just for addition but also for multiplication and division mental strategies.
With regular use the students will instantly recall compliments of 10 (e.g., 4+6, 2+8, etc) and this knowledge becomes a powerful ally in mental addition and subtraction calculations.
Tens frames can also be used to model decimal fractions where the whole frame is called "one" and each space is one tenth (because "tenths are formed when a whole is divided into ten equal parts"). So 4 dots on the frame shows four tenths, or 0.4. Students can then quickly move from naming and modelling decimal fractions to adding them without having to rely on an algorithm being taught.