Recommendation letters

One of my former students recently asked me to write a recommendation letter for her because she was applying for a scholarship. I wrote the letter for her not just because she had gotten high grades in my class, but also because she gave me enough time to write the letter. The scholarship application deadline was still more than three weeks away.
I often get asked by students to write recommendation letters; they apply for scholarships, graduate schools, study abroad programs, and internships. To be honest, I think that they should ask professors who are full-time or tenured, not a part-time adjunct instructor or a teaching assistant like me, because the word of the tenured professors often carry more weight than mine do. Also, it's better to get a letter from someone who actually works in the field that you want to work in. I teach freshman composition and literature courses, and most of my students aren't English majors. The classes I teach generally fall into the "general education" category; the students are required to take them in order to graduate.
But if the student did well in my class, I'm usually willing to write a recommendation letter for him or her. Usually. I have said no to a few students, however, even if they did get good grades in my class. The number one reason is I often just don't have time. For the past several years I've always worked at least two jobs, sometimes three. And now that I'm working on my Ph.D. in addition to my part-time jobs, my free time is very limited.
Writing a recommendation letter is a lot of work. It's not like I can write the same letter for every person. Well, I could, but that wouldn't help the student very much. The letter is important because it lets the admissions committee know why this student is qualified and what he or she is like to work with. It highlights specific qualities this student has, and describes accomplishments this person did in my class. So it takes a lot of time to come up with a good letter, even if that letter is only one or two pages. I want to write good letters in order to help students get whatever it is they're applying for.
That's why I need to be given enough notice in order to write the letter. I had one student e-mail me a request for a recommendation, but he said that the letter was due the next day so he needed it ASAP. That bothered me to no end, because he just assumed that I would be able to drop everything and work on the letter. But I couldn't. So I told that student that I couldn't write the letter because I was busy with my other work, which was true. Other students try to pressure me or guilt me into writing the letters for them, saying that they've asked other professors who turned them down and that they need enough letters in order to get whatever it is they're applying for. But in those cases, the other professors probably said no because they weren't given enough time to work on the letters.
When I was an undergrad, none of my professors would have even considered writing a letter for me if I hadn't given them at least two weeks' notice; some of them required a month. So I always made sure to give them enough time.
The thing about a recommendation letter is that, in a way, it's a favor that the teacher does for the student. I'm happy to help my students, but I'm not always available to help them with everything at a moment's notice. And even if I did have unlimited free time, I feel it's important to teach students to be responsible and considerate.