Why are some words (e.g., 処方箋) sometimes partially written with hiragana?


Some words with complex Kanji are sometimes written in a mixture of Hiragana
and Kanji. For example 処方箋 (prescription) is often written as 処方せん in
pharmacies. This is used by native speakers that have clearly received a
Japanese education and can read Kanji, yet they still use Hiragana in some
cases.

What are the reasons for the use of Hiragana here? Are Japanese people able to
read Kanji like 箋? What contexts would they use Hiragana instead? Why is it
acceptable to use Hiragana mixed with Kanji but not Katakana?

Is this kind of usage limited specifically to signs in stores that can be read
at a distance or is it written in kana in other contexts as well?

