You can use GIMP for professional needs, including image editing to print. But first, there are some settings you need to make. One of which, you need to set the color space to Adobe RGB. While this setting is not required, using Adobe RGB provides better color accuracy so that the colors you see on GIMP will not different from the ones you see on the paper once the image is printed.
If you are editing an image for a printing purpose, using Adobe RGB is highly recommended since this color space has a wider range of colors (color gamut) compared to sRGB, the default color space of GIMP. Adobe RGB encompasses 50% of the visible colors specified by the CIELAB color space, while sRGB encompasses only 35%. You can read this Wikipedia page to learn more about why this Adobe RGB is better than sRGB.
How to add Adobe RGB in GIMP
To add Adobe RGB in GIMP, you need to download the ICC file of the Adobe RGB first. You can download it here. The file is available for Windows, Mac, and Linux. Select the platform you use by clicking a link on the bottom side.
On the next page, click the ICC profile download for End Users link.
On the next step, accept the user license agreement and click the Proceed to Download link to download the ICC file (available in a ZIP format).
Once the ZIP file is downloaded, extract it. The file you need is AdobeRGB1998.icc. This file lies under the RGB folder.
On the GIMP window, open the Preferences window (Edit -> Preferences) and click Color Management on the left side. On the right side, scroll down to the Preferred Profiles section and click the dropdown menu on RGB profile and select Select color profile from disk. Navigate to the location where you saved the AdobeRGB1998.icc file.
Click the OK button to save the change. Make sure to not delete the AdobeRGB1998.icc file. If you accidentally delete it, you can repeat the steps above to re-add Adobe RGB in GIMP. You can save the AdobeRGB1998.icc anywhere. To avoid accidental deletion, you can save it to a folder that you rarely touch it.