Source code is read by both the compiler, which doesn't care about your writing style, and people, who care enormously about your writing style.
ALL programmers insist that certain rules be followed. Some of the most important are:
Instructor. If you're taking a programming course your instructor will care a lot about the indentation and meaningful names. Some instructors have a specific class standard for formatting your program. Others allow a range of standards. None allow chaotic code formatting.
Other programmers. If you work on a project that will ever involve other programmers, eg, for maintenance, you must write in a conventional style. Multi-programmer projects often establish a set of standards for all programmers on the project.
Yourself. Surprisingly many student programs use meaningless, deceptive, or multiple-use variable names. When asked what value is in that variable, they are often unable to tell me. Variable names should mean something clear to to the reader.
The problem with tabs is that there is no single definition of how much horizontal space a tab takes, so what you see in your program may be (and often is) very different from what I see when I look at your program. The indentation may be consistent, which isn't so bad, but if you tab to the comments then it usually doesn't work so well when I look at it. And the worst is mixing tabs and spaces because a change in the tab size guarantees things will not be correctly aligned. The programming convention for Java is to use 4 spaces.